Rosetta Code

Palindromic primes: Difference between revisions

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→‎{{header|ALGOL 68}}: Use ALGOL 68-primes
m (→‎{{header|REXX}}: changed the GENP subroutine.)
(→‎{{header|ALGOL 68}}: Use ALGOL 68-primes)
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=={{header|ALGOL 68}}==
Generates the palindrmic 3 digit numbers and uses the observations that all 1 digit primes are palindromic and that for 2 digit numbers, only multiples of 11 are palindromic and hence 11 is the only two digit palindromic prime.
{{libheader|ALGOL 68-primes}}
<lang algol68>BEGIN # find primes that are palendromic in base 10 #
INT max prime = 999;
# sieve the primes to max prime #
PR read "primes.incl.a68" PR
[ 1 : max prime ]BOOL prime;
prime[ 1 ] := FALSE;BOOL prime[ 2= ]PRIMESIEVE :=max TRUEprime;
FOR i FROM 3 BY 2 TO UPB prime DO prime[ i ] := TRUE OD;
FOR i FROM 4 BY 2 TO UPB prime DO prime[ i ] := FALSE OD;
FOR i FROM 3 BY 2 TO ENTIER sqrt( max prime ) DO
IF prime[ i ] THEN FOR s FROM i * i BY i + i TO UPB prime DO prime[ s ] := FALSE OD FI
OD;
# print the palendromic primes in the base 10 #
# all 1 digit primes are palindromic #
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